Diagraming your applications can be a useful exercise. It can give you a chance to think clearly about what already exists, what you plan to create and how it will work. Some of the best systems I’ve designed were complete mysteries to me, then I took time to diagram what already existed and it helped me see what needed to be created next. Diagrams can also be extremely valuable documentation, even if they are slightly out of date. I recommend a tool called Excalidraw for creating technical diagrams.